Perhaps Jacob could start to spread negative rumors about Bella among their mutual friends. This would create a rift not only between them but also within the larger group that they are a part of. He may feel betrayed by Bella for some reason and wants others to see his side.
There could also be other characters from the Twilight series involved. For example, the members of Jacob's wolf pack might play a role. They could be trying to mediate between Jacob and Bella, or they might side with Jacob, adding more tension to the story.
One reason could be that Jacob realizes they have different life goals. Bella is often so focused on Edward and the vampire world, and Jacob may feel that his werewolf life and values are too different from hers to have a romantic connection. For example, he might want a more traditional werewolf life with his pack, while Bella is constantly drawn to the dangerous and alluring vampire lifestyle.
In fanfiction, a scenario could be that the Cullens exclude Bella from important family decisions. This makes her feel like an outsider and unloved. Or perhaps they try to manipulate her into doing something she doesn't want to do, such as leaving her human friends behind. This would lead to her not forgiving them.
In some fanfiction, Bella might not forgive the Cullens because of a perceived betrayal. For example, if they hid something crucial from her again. It could also be due to them putting her in danger without her consent. Another reason could be a broken promise related to her transformation or her relationship with Edward.
In a 'Jacob cheats on Bella with Leah' fanfiction, the plot might start with Jacob feeling neglected by Bella who is still somewhat hung up on Edward. Leah, on the other hand, is there for Jacob, and they gradually get closer. This closeness turns into an affair, and when Bella discovers it, there could be a big fight. Bella might be heartbroken and seek revenge, or she could try to win Jacob back. Meanwhile, Jacob has to deal with his guilt and the consequences within the pack as his actions could affect pack dynamics.
Perhaps in the fanfiction, Edward broke a significant promise to Bella. Promises are important in relationships, and if he failed to keep one, it could lead to her not forgiving him. For example, if he promised to always be there for her but then abandoned her in a time of need. Also, his over - protective nature in a wrong way could make Bella feel suffocated and less likely to forgive him.
Well, in some Jacob and Bella lemon fanfiction, there's a plotline where they are forced to work together on a project for the reservation. This makes them spend a lot of time together and they start to see each other in a new light. Another plot might involve Bella getting injured and Jacob being the one to take care of her. During this time, their relationship deepens in a more tender and affectionate way. There are also stories where they discover a shared interest in a particular art form or hobby and bond over it.
One interesting plotline could be their adventures in the forest together. They might discover a hidden part of the forest that has some kind of magical or ancient significance. Another could be them dealing with the reactions of their respective families and friends to their relationship.
In some fanfictions, Bella might be involved in a community project where she meets Jacob again after a long time. Their shared values in helping the community bring them closer, and they start to see each other in a new light. This could lead to a sweet and slow - burning romance.
A possible plotline could be that Naruto is sent on a mission where he has to deal with a group of people who communicate solely through emotions. Since he doesn't understand emotions well, he struggles to complete the mission. Another one is that he tries to form a closer bond with Sasuke, but his lack of emotional understanding keeps creating misunderstandings between them.